I've had a Begonia Rex that cuttings of which have been in my family for generations, so it is extremely important to me that I keep it alive and happy. My cat seems to think otherwise. So after he knocked off one particularly nice leaf, I decided to try propagating it as I had been reading about, slicing across the veins and laying it in soil in a little covered seed tray. It worked beautifully, tons of little wonderful new plants, but I can't seems to keep them alive transplanting them. I've tried replanting three promising little plants, and each have rotted and died. I can find a million instructions on how to propagate this way, but no advice on what I might be doing wrong. I've been waiting until they look healthy and the leaves are getting close to the top of the clear plastic cover, then just digging them out and putting them in well-drained potting soil. Any advice?